Process for hardening colloids



m an June 10,1930

' ALFRED MILLER, or nnssav, GERMANY, assrenon, BY MESNE Assmmrmv'rs, r

AGFA nnsco CORPORATION, NEW YORK QF'BINGHAMTON, NEW -YORK, A CORPORATION OF raocnss non. HARDEN-ING connorns i No Drawing. App'lica tion filed February 2, 1924, Serial No. 690,325, and in Germany November 27,1923.

In the application of colloids, such as casein, gelatine, agar-agar, gum arabic or the like in industry, it is frequently necessary to harden them and for this pilrpose there are 6 used in general materials like alum, aldehyde, quinone, tannin and other tanning materials,

in short, substances which in a single operation harden colloids or make them insoluble. Another hardening procedure, which is 10 adopted for example in the art of printin consists in subjecting a bichromatized co loid layer, such as'a gelatine layer, to the action of light. As is well known, bichromates are chromium -salts which do -.not

harden gelatine. It i'sonly by the action of:

light that the bichromate undergoes a change, as the result of which chromic salts are produced which exert a'hardening action ongela- V tine. If while being exposed. to light the bichromatized colloid layer is shielded by a photographic negative having a. silverdeposit of varying density, the amount of chromic salts produced inthe colloid layer varies in an inverse proportion to the densities of the negative. Thus by the varying amountsof chromic salts a picture composed ofdifi'erently hardened areas is produced on a the colloid layer (collotype and pigment processes). Accor'ding to the present invention the action of chemicals havin a similar ef feet is made use of instead of the action of light.

As is well known to those skilled in the art, gelatine layers which have been treated. with a hardening agent, such as formalde-,

, hyde, chrome-alum or the like, present a very great inconvenience, because in the course of time they undergo a further hardening, which is undesirable and which is caused by storage conditions and the like and which cannot be prevented nor controlled. By this further hardening the properties of the stock'are changed in such a manner that it is .no longer suitable for the particular-purpose for which it is intended-as for example, the production of a relief by swelling. The present invention relates to a new method of hardening which overcomes this inconvenience. Since it is not advantageous to harden the colloid prior to storage due to the further invention are:

ers do not like to perform the entire harden ing operation themselves immediately before use, the hardening procedure is divided into two operations accordmg to the present invention. The first operation, WhlCll may be called a reparatory one, is carried out during the abrication of the colloid, while the second operation, the hardening o eration' properly so-called, is carried out onl immediately efore use. Between these two operations there may be a considerable lapse of time. The first operation consists in incorporating with the colloid substances which are not hardening agents per se but which produce hardening agents by areaction with other substances which also are not hardenin agentsper se and which are added to the.

co loid in the second operation. V

Thus the essential features of the present 1. The hardeningof the colloid by a hardening agent produced in or on the colloid by the reaction of two substant'es each of which is not a hardening agent per se and which are not-incorporated with the colloid simultaneously but at difierent times inseparate operations;

'2. The hardening of thescolloid in two separate operations in which the lapse of time between the two operations may be of any length desired and of which operations on y the second one initiates the hardening.

It has alreadybeen proposed heretoforeto harden colloids b incorporating in them two substances w ich by reaction form a hardening agent, but these substances were added at once and together, the hardening thus being produced immediately during the fabrication of the colloid mass. A hardening process likethat of the present invention, in which the two substances are added at difierent times so that the hardenlng ma be initiated at any desired time, has not can disclosed heretofore. g a g The hardening can be controlled 1n any desired-manner by varying the proportions of material originally added. For example, there may be added to a gelatine layer a su1t-' able reducing agent which does not of itself harden the gelatine and when the layer is to be further treated .it may be introduced This process is useful in many ar ts among others in the treatment of spun threads, in

the production of films from plastic'masses,

in the art of reproduction.

In order to improve the adhesion of the colloid printing layeron its support (glass,

paper. celluloid or the like) it has been proposed in the graphic art to subject thelayer sensitized with bichromate to a short exposure to diffused light through the support and then to perform the usual copying operation. In particular this is said to be neces sary in making colloid printing layers on a to the trouble it involves, the disadvantage that it affects the character of a picture in an uncertain and uncontrollable manner. according to the degree of the .action of the light, the transparency of the support. the

thickness of the layer and the like. If in consequence. of inattention the illumination is protracted, the .copy'maybe completely ruined. If there be particles of dirtior spots .of dried sensitizing agent (for' example bichromate,-which new acts as a yellow filter for light) on the back of the supporh'the printing layer comes away from the support layer at those places which-have not been sufl'iciently illuminated. In many cases illumination from the back is precluded. for

ms ance m t 0 case of Opaque qimpm'tq of hardnlng thG'COllOld by itself. This metal), supports which are not uniformly translucent (paper of strong-structure). or when the support has matter on its back which makes it-opaque. The chemical process in this illumination through the back consists in a gradual and continuous strong hardening of the part of the sensitized layer which is adjacent to. the support. so that for the further treatment of the printing plate 5' the layer is damaged in respect of its capacity for swelling and as a consequence it adheres to the support.

When it'is attempted to substitute for the; back illumination avhardened intermediate layer on which the main layer is afterwards formed or deposited, the two layers do not" unite together. When, however, the intermediate layer-is hardened in the manner which causes the two layers to adhere firmly toforms the subj ect matter of this invention it gether in ,consequenceof certain difiusion phenomena; i v

It is also possibleto harden'the whole of the printing layer according to the lnvention.

If the hardening does not extend over the whole surface of-the printing layer but is locally limited, a clich may be vobtained directly fit for flat printing processes. If, ho wever, the unhardened colloid is washed away the cliche may be used for relief printing. Having produced by the new process a hardened colloid relief on a metal support and having removed the unhardened colloid the metal may be etched in order to obtain for instance a clich for intaglio printing.

The following examples without limiting the inventionillustrate how the process can be performed. Of course. the particulars may be varied within wide limits. any suitable colloid in any suitable form being -em-- ploycd as well as other hardening agents' formed by reacting with non-hardening sub,- stances of any kind of non-hardening substances of any kind previously incorporated into the colloid;

I am aware that it has alreadybeen proposed to incorporate into gelatine bichromates of ammonium or of potash, which do not immediately exert a hardeningaction on gelatinc. However, it is well known to those skilled in the art that bichromatized gelatine undergoes an undesired hardening within a few days due to a slow decomposition of the bichromate salt occurringwithout any in-- fluence of other substances or of light.

Hence I do not contemplate the use of bichro mate as a substance to be uniformly distributed in a colloid and to be acted upon later by another substance to produce a-hardening agent. Bicliromates may. however,'be applied in my process as second substance which, to produce an immediate hardening agent, is added to a colloid containing in uniform distribution a substance not capable is spread on a suitable support and dried.

I When it is immersed in a bath consisting of 3 grams of potassium'bichroniate dissolved in grams of 'water there is immediate formationof ferric salt and chrome compound both of which give rise to a controlled hardening of the gelatine layer. i

Ewamgl'e 2.On celluloid there is spread a liquid w i'ch contains one per cent of hydroquinone in addition to the usual solvents for celluloid andgelatine. When the layer has been dried it-is coated with a solution of gelatine. When the gelati'ne layer is sensitized with potassium bichromate as recited above there is produced between the materials used a, reaction, the consequence of which is a firm adhesion of'the printing layer to the t celluloid; Example 3.There is spread on a celluloid .film, prepared as usual, a layer a few thousands of a millimeter thick of elatine containing 2 per cent of formaldehy e bisulphite. When the layer has been dried there is cured upon it the usual printing layer suita 1e for a photomechanical process When this printing layer is dry it is treated with a 5 per cent solution of alkali whereb the formaldehyde bisulphite is decompose and the liberated formaldehyde hardens the intermediate layer,

so that there is an adequate adhesion of theprinting layer in use in printing. Example 4.-A elatlne solution is mixed with 2 per cent 0 h droquinone and is allowed to set in any orm, for instance as a thin layer, and dried. When the layer is. treated with otassium bichromate as recited above throug out its mass'or locally, for instance. in written character, ther'eis an instantaneous formation of quinone and chrome compound and consequently a hardening of the gelatine at the places treated. If, for instance writing is. reduced in this manner by. stamping on age atine layer this layer may. afterwards be used in 'known manner for printing according to the usual photographic printing processes. The -gelatin'e layer neces-' 40 sary for such a process may vary in its thickness between wide limits. Example 5.-A web ofanimalor vegetable fibres or of artificial fibres (paper or the like)- is saturated with a gelatine solution containing 5 per cent of formaldehyde-sulfoxylate it is afterwards immersed in a 5 per cent bath of potassium bichromate whereupon the gelatine is immediately. hardened and the web is permanently impregnated therewith. y j i It is of cpurse understood that the invention is not limited inany way tothe specific ma-' terials, manifiglations or proportions recited in the prece g examples.

Having now described myiinvention what I claim 1s, r. v

1. The process which comprises treating 'with a solution qf an alkali e layer containing formaldehyde bi 2. As a composition of'inatter a elatine layer containing formaldeh de bisul te'. In'testimony whereof I a x my si ature. ALFRED MIIZfiER. 

